1. Field of the Invention
The present invention relates to a piezoelectric actuator and a liquid-droplet jetting head.
2. Description of the Related Art
As a conventional ink-jet head, there is known an ink-jet head having a cavity unit which is constructed by stacking a plurality of sheets and which has a plurality of pressure chambers formed and aligned in a plurality of rows therein, and a piezoelectric actuator which has active portions (energy-generating mechanism) corresponding to the pressure chambers respectively and which is joined to the cavity unit. There is known a piezoelectric actuator in which a plurality of ceramic sheets are stacked; the ceramic sheets includes a ceramic sheet having a plurality of individual electrodes formed thereon, a ceramic sheet having a common electrode which is formed thereon, which is common to the individual electrodes and which is arranged to face the individual electrodes, and a ceramic sheet stacked on the uppermost layer and which has surface electrodes formed on a surface on the ceramic sheet and connected to the individual electrodes and another surface electrode formed on the surface on the ceramic sheet and connected to the common electrode; and in which connection terminals of signal lines of a flexible flat cable, via which a driving signal is inputted, are connected to the surface electrodes and the another surface electrode. For example, see U.S. patent application Publication No. US2005/162484A1, U.S. patent application Publication No. US2005/248628 (corresponding to Japanese Patent Application Laid-open No. 2006-15539), and U.S. Pat. No. 6,595,628 (corresponding to Japanese Patent Application Laid-open No. 2002-254634).
Further, the piezoelectric actuator described in U.S. patent application Publication No. US2005/162484A1 and U.S. patent application Publication No. US2005/248628, a ceramic sheet having a connection pattern for connecting the surface electrodes and the individual electrodes is formed thereon is stacked between the ceramic sheet having the surface electrodes are formed thereon and the ceramic sheet having the individual electrodes formed thereon. In such a piezoelectric actuator, through holes penetrating through the ceramic sheets are formed and an electrically conductive material is filled in the through holes, thereby realizing the connection among the individual electrodes and the connection pattern and the surface electrodes.
On the other hand, in the piezoelectric actuator described in U.S. Pat. No. 6,595,628, the through holes are arranged so that the through holes are not arranged in one row in a direction parallel to an arrangement direction of the individual electrodes, to thereby suppress the arching deformation or warpage of the ceramic sheets, with the through holes as the base point of the arching deformation, which occurs during calcination process.
Further, the piezoelectric actuator described in U.S. patent application Publication No. US2005/162484A1, U.S. patent application Publication No. US2005/248628 and U.S. Pat. No. 6,595,628 requires a flexible flat cable in which a large number of terminals connected to a large number of surface electrodes respectively, and a large number of signal lines drawn from the terminals respectively are arranged or wired on a flat surface of the flexible cable. Therefore, in order to prevent these terminals and wirings from interfering each other and to make spacing distance among the signal lines as large as possible, it is necessary to broaden spacing distance between the terminals as much as possible. To realize the broad spacing distance, it is necessary to arrange the surface electrodes such that a spacing distance is present between the surface electrodes. In the piezoelectric actuator described in U.S. patent application Publication No. US2005/162484A1 and U.S. patent application Publication No. US2005/248628, the surface electrodes are arranged in a plurality of rows in a row direction at a arrangement pitch such that surface electrodes in a certain row are shifted, by half the arrangement pitch with respect to surface electrodes in another row adjacent to the certain row.
Further, in each of the rows of the surface electrodes, positions at which the surface electrodes are connected to the signal lines of the flexible flat cable respectively are located alternately at both end portions of the surface electrodes, the both end portions being orthogonal to the row-direction of the surface electrodes.